Oh.
Hey. A thing. I'll just quietly sneak in.
EDIT: Okay, super rough five minute idea for Atlantis, since I see that that is a thus far unused archetype:
Atlantis was a grand city in the early days of humanity, when gods were still worshiped and strong. They were the first civilization to "invent" magic, and the gods that ruled the world at the time were angered and frightened of the power that mortals were showing. They tried to put a stop to it early, and the gods of earth and water joined forces to sink the entire city into the ocean. The Atlanteans protected themselves with their magic, and survived the calamity, but deep in the ocean the only god who knew of their survival was the ruling ocean god of the time. This god kept their continued existence a secret from the others, meaning to use the magical power of Atlantis for his own means later.
The Atlanteans summoned storms at sea for the Ocean Father, and helped guide the waves and twist the creatures of the deep into more powerful or more cunning monsters than ever. The shift in power to the Ocean created mistrust between the gods of the time, and when the time came that the Ocean called on Atlantis to aid him in a bid for power, they agreed. But they lied. When the Ocean Father made his move, Atlantis stayed hidden in the deeps, and let the gods tear each other apart, reveling in their long awaited revenge.
But this was many thousands of years ago, and the Magi of Atlantis have urged their people to stay hidden all this time. It was only recently, when the first scouts in thousands of years dared to surface that the Atlanteans discovered that the world they had known had been replaced by the modern age. Gods may still exist, but the truly powerful beings were mortals. This was the age that Atlantis was meant to live in. They revealed themselves, and lifted the city, not all the way to the surface, but out of the deepest depths that they had been hiding in.
Physiology: Because of a lack of population, Atlantis has used magic to re-diversify their genes to prevent inbreeding, and to make them more fit for their new home. Atlanteans are pale as a general rule, all have gills and all are stronger and tougher than an average human(a result of living at extreme pressures). Some retain their human shape, but many come from more heavily altered bloodlines and have bodies more suited for moving in water. All Atlanteans are amphibious, however, as the main portion of the city exists in a bubble.
EDIT 2: Eh, on second thought, I don't want to play an ocean based character in a mountain town.